<template>
  <scroll class="listView"
          :data="data"
          ref="listView"
          @scroll="scroll"
          :probe-type='probeType'
          :listen-scroll="listenScroll"
  >
    <ul>
      <li v-for="group in data" class="list-group" ref="listGroup">
        <h2 class="list-group-title">{{group.title}}</h2>
        <ul>
          <li v-for="item in group.items" class="list-group-item" @click="selectItem(item)">
            <img class="avatar" :src="item.avatar"/>
            <span class="name">{{item.name}}</span>
          </li>
        </ul>
      </li>
    </ul>
    <div class="list-shortcut" @touchstart="onShortcutTouchStart" @touchmove.stop.prevent="onShortcutTouchMove">
      <ul>
        <li v-for="(item,index) in shortcutList"
            class="item" :data-index="index"
            :class="{'current':currentIndex===index}"
        >
          {{item}}
        </li>
      </ul>
    </div>
    <div class="list-fixed" v-show="fixedTitle" ref="fixed">
      <div class="fixed-title">{{fixedTitle}}</div>
    </div>
    <div v-show="!data.length" class="loading-container">
      <loading></loading>
    </div>
  </scroll>
</template>

<script type="text/ecmascript-6">
  import Scroll from '../scroll/scroll'
  import {getData} from "../../common/js/dom";
  import Loading from '../../base/loading/loading'

  let _this = null;
  //右边字母哪一行每个字母的height
  const ANCHOR_HEIGHT = 18
  const TITLE_LENGTH = 30
  export default {
    created(){
      this.touch={}
      this.probeType = 3
      this.listenScroll = true
      this.listHeight = []
    },
    props: {
      data :{
        type:Array,
        default:[]
      }
    },
    data(){
      return {
        scrollY:-1,
        currentIndex:0,
        diff: -1
      }
    },
    mounted () {
      _this = this;
      _this.init();

    },
    methods: {
      init () {
      },
      refresh(){
        this.$refs.listView.refresh()
      },
      selectItem(item){
        //把点击事件派发出去
        this.$emit('select',item)
      },
      onShortcutTouchStart(e){
        // console.log(e) ========= e.target得到的是那个li，从而得到index的值
        let anchorIndex = getData(e.target,'index')
        //一开始触摸的位置
        let firstTouch = e.touches[0]
        this.touch.y1 = firstTouch.pageY
        this.touch.anchorIndex = anchorIndex
        this._scrollTo(anchorIndex)
      },
      onShortcutTouchMove(e){
        let firstTouch = e.touches[0]
        this.touch.y2 = firstTouch.pageY
        //移动了几个索引
        let detail = (this.touch.y2 - this.touch.y1) / ANCHOR_HEIGHT | 0;
        let anchorIndex = parseInt(this.touch.anchorIndex)+detail
        this.$refs.listView.scrollToElement(this.$refs.listGroup[anchorIndex],0)
        this._scrollTo(anchorIndex)
      },

      _scrollTo(index){
        // this.scrollY = -this.listHeight[index]
        if(!index && index!==0){
          return
        }
        if (index < 0) {
          index = 0
        } else if (index > this.listHeight.length - 2) {
          index = this.listHeight.length - 2
        }
        //点击时会高亮显示
        this.scrollY = -this.listHeight[index]
        this.$refs.listView.scrollToElement(this.$refs.listGroup[index],0)
      },
      refresh(){
        this.$refs.listView.refresh()
      },
      //scroll.vue监听到的实时值传给this.scrollY
      scroll(pos){
        this.scrollY = pos.y
      },
      _calculateHeight(){
        let height = 0;
        this.listHeight.push(height)
        const list = this.$refs.listGroup
        for(let i=0; i<list.length;i++){
          let item = list[i]
          height += item.clientHeight
          this.listHeight.push(height)
        }
      },
    },
    watch: {
      data(){
        setTimeout(() =>{
          this._calculateHeight()
        },20)
      },

      //计算滚动的位置    newY 是等于  pos.y
      scrollY(newY){
        // console.log(newY)
        const listHeight = this.listHeight
        //当滚动到顶部的时候
        if(newY>0){
          this.currentIndex = 0
          return this.currentIndex
        }
        //当滚动到中部的时候
        for(let i =0;i<listHeight.length-1;i++){
          let height1 = listHeight[i]
          let height2 = listHeight[i+1]
          if(-newY>=height1 && -newY<height2){
            this.currentIndex = i
            this.diff = height2 + newY
            return this.currentIndex
          }
        }
        //滚动到底部的时候
        if(this.currentIndex === listHeight.length - 2){
          return this.currentIndex
        }
      },
      //title之间的差值
      diff(newval){
        //计算两个title之间的差值
        let fixedTop = (newval >0 && newval< TITLE_LENGTH) ? newval - TITLE_LENGTH : 0
        if(this.fixedTop === fixedTop){
          return
        }
        this.fixedTop = fixedTop
        //给title的style赋值
        this.$refs.fixed.style.transform= 'translate3d(0,'+this.fixedTop+'px,0)'
      }

    },
    components: {
      Scroll,
      Loading
    },
    computed: {
      shortcutList(){
        return this.data.map((group) =>{
          //热门只有一个字
          return group.title.substring(0,1)
        })
      },
      fixedTitle(){
        if(this.scrollY>0){
          return ''
        }
        return this.data[this.currentIndex] ? this.data[this.currentIndex].title : ''
      }
    },

  }
</script>


<style lang="stylus" rel="stylesheet/stylus">
  @import '../../common/stylus/variable.styl';
  .listView
    position: relative
    width: 100%
    height: 100%
    overflow: hidden
    background: $color-background
    .list-group
      padding-bottom: 30px
      .list-group-title
        height: 30px
        line-height: 30px
        padding-left: 20px
        font-size: $font-size-small
        color: $color-text-l
        background: $color-highlight-background
      .list-group-item
        display: flex
        align-items: center
        padding: 20px 0 0 30px
        .avatar
          width: 50px
          height: 50px
          border-radius: 50%
        .name
          margin-left: 20px
          color: $color-text-l
          font-size: $font-size-medium
    .list-shortcut
      position: absolute
      z-index: 30
      right: 0
      top: 50%
      transform: translateY(-50%)
      width: 20px
      padding: 20px 0
      border-radius: 10px
      text-align: center
      background: $color-background-d
      font-family: Helvetica
      .item
        padding: 3px
        line-height: 1
        color: $color-text-l
        font-size: $font-size-small
        &.current
          color: $color-theme

    .list-fixed
      position absolute
      top:0
      left:0
      width 100%
      .fixed-title
        height 30px
        line-height 30px
        padding-left 20px
        font-size $font-size-small
        color $color-text-l
        background-color $color-highlight-background
  .loading-container
    position: absolute
    width: 100%
    top: 50%
    transform: translateY(-50%)
</style>
